Nozzle Penetration through Blind Flange

[babman]

First post on here, so be gentle with me!
Can't say enough good things about this forum - especially for a young engineer - it has given me lots of design pointers and guidance in some tricky situations.

I was wondering if I could gather some advice on placing a nozzle penetration through a 8" blind flange.
I have been given varying advice from other engineers in the office on a design and would like some other guidance.

I have a classic cylindrical pressure vessel, vertically mounted with 2:1 elliptical heads.
The design has been used for several years on a skid unit, but there is an issue with the demister pad installed internally in the upper section of the vessel.
Our warranty engineers have either had to cut the vessel to remove these pads or dissemble a lot pipework for access.
Essentially to cut a long story short, the plan is to change a 1 1/2" nozzle in the centre of the upper head, to a 8" nozzle to allow access for removing the pad.

So far, following Lloyds Register (marine contract) and ASME B16.5, I have replaced the 1 1/2" inch RFWN 300# flange, with a 8" equivalent, stuck on a blind counter flange and I'm now trying to put the 1 1/2 nozzle through the blind flange, to connect with the associated piping.
Just wondering if there is a section of either Lloyds or ASME I should be looking at for guidance on penetrating a blind flange with another nozzle/pipe. The pipework is SCH 80 wall thickness.

One engineer suggested treating the blind flange as another vessel wall thickness and simply doing an area of replacement calc and another disagrees entirely and suggests instead of the blind flange, do a flanged reducer.
The only problem is we are going from 8" down to 1 1/2" so I would think we would need 2 reducers to do this. Considering the height of the vessel is just over 2 m, this would mean the nozzle will be sitting way higher than it currently is. The PV is sitting on a skid to be fitted in a compressor room on a LPG carrier - so we have restricted height between decks.

Any help/guidance would be much appreciated!

Design Pressure 18 bar
Shell and Head thickness 9mm Carbon Steel
Design Temo -52/+60 degree C

 

[pdiculous963]

Per Table 6 of B16.5 pipe sizes below NPS 3 do not require hubbed flanges for a NPS 8 blind. Based on that that there is no calculations required to put a NPS 1.5 pipe in a NPS 8 blind. I would size the welds per figure UW-21 of Sec. VIII-1 if you are going to weld like a slip on or UW-16 if it is going to be full penetration.

 

[TomBarsh]

I agree with pdiculous963.

Assuming rules similar to ASME VIII-1, see the discussion in the Hartford Steam Boiler (HSB inspection company) 's "Pressure Points" quarterly newsletter, June, 1999. See the first Q/A on page 1.

http://hsbglobalstandards.com/uploadedFiles/CTWeb/AllImages/PP-1999-06.pdf

The "answer" makes full sense to me except that the very last remark seems unnecessary and is confusing to me. They state "Per UG-39(a) and UG-36(c)(3)(c) of Section VIII, Div. 1, the finished opening [2.09” I.D.] is exempt from reinforcement calculation."

My view is that the B16.5 blind flanges are accepted by UG-44, so even if the opening was larger than that permitted by UG-36(c)(3)(a) the blind with opening would still be accepted without further calculations based on it being accepted under UG-44 and it being a standard variation permitted/described in B16.5.

 

[BJI]

Yep pdiculous963 has your answer. I also agree with Tom's interpretation, they can be used within the limits of B16.5 without calculation.

 

[r6155]

For -50ºC see UCS-68.

Regards
r6155

 

[marty007]

Just to expand on your other engineer's recommendation of a flanged reducer, one option in B16.5 is a "reducing flange". This is a one-piece reduction from one size to another (no butt-weld reducers).

See B16.5 paragraph 6.8

One supplier's description: Link

 

[rtmorgan]

I may be the odd guy out, but have you considered machining a 1-1/2" Flange surface/gasket surface/drill & Tap bolt holes in the blind? Blind thickness would have to be looked at, but you save at least one if not two welds.

Good luck
Rick

 

[XL83NL]

Reducing flanges are interesting, but to our experience very expensive; they are almost always custom made. I would stay away from them as long as you can and only use them when you have to, i.e. according B16.5 table 6.

 

[babman]

Thanks for all the replies.

Definitely the advice I was looking for!

 

[BJI]

@rtmorgan, this would be a custom flange design and likely couldn't be made from a standard blind. It is also a studded connection which isn't preferable to through bolted joints. I would rather weld it, and by the time you add up the work involved in designing and machining the blind I think you will still be ahead by welding.